Martensitic Transformation and Magnetocaloric Effect in Co-Doped Ni–Mn–In Ferromagnetic Shape Memory Alloy

In this work, we present the detailed results of magnetic, structural, and magnetocaloric measurements in Ni-Mn-In-based Heusler alloys, namely, Ni
₅₁
Mn
_32.8
In
_16.2
, Ni
_50.2
Mn
_33.6
In
_16.2
, and Ni
₅₁
Mn
_33.4
In
_15.6
. The characteristics of magnetostructural coupling play an important role in the magnetic field-driven behavior of these alloys. A small variation in the stoichiometry composition broadens the magnetic entropy change curve and shifts the critical temperatures by as much as 48 K. The effect of cobalt doping on the magnetic, structural, and magnetocaloric properties in these multifunctional alloys is investigated through characterizing Ni
₅₀
Co
₂
Mn
₃₅
In
₁₃
and Ni
₄₅
Co
₅
Mn
₃₇
In
₁₃
samples. Cobalt doping affects the martensitic and magnetic transformation temperatures and enhances the ferromagnetic properties of the parent austenitic phase. Therefore, the magnetization change accompanying the martensitic transformation is significantly improved, resulting in a large magnetic entropy change of 21.6 J kg
^-1
K
^-1
at 1.5 T. Additionally, Co doping broadens the operating temperature window to 21 K around room temperature. Consequently, a significant effective refrigeration capacity of 254 J kg
^-1
for 1.5 T is obtained which is comparable or even superior to that of the high-performance, though expensive, rare-earth-based magnetocaloric refrigerants. The high performance, low cost, nontoxicity, and tunability make these alloys of great interest and promising prospect for an affordable magnetic refrigeration system.